In particular, yet not restrictive manner, the invention concerns a mechanical locking system for rectangular floor panels with long and short edges. Such floor panels are generally installed with an angling of long edges. Short edges could be connected with angling, horizontal snapping or insertion along the short edge. The installation requires three actions since a displacement in locked position is also required to lock all four edges.
It is also known from US 2003/0101681 A1 that a locking system could be formed on the short edge with a tongue and a groove comprising projections and indentations such that the short edges could be moved horizontally into contact and thereafter displaced along the short edges and locked. The long edges are thereafter locked with angling. This locking system and installation method is based on the same principles as the known insertion of the sort edges. The only advantage is that the displacement of the short edges could be reduced from about 0.1-0.2 m (the width of conventional floor panels) to some centimetres and this small advantage is generally eliminated by the additional costs to form the projections and indentations with the type of machining that is used in floor production. Such locking systems are not used on the market.
It should be emphasized that long and short edges are only used to simplify the description. The panels could also be square, they could have more than 4 edges and the adjacent edges could have angles other than 90 degrees. However, the invention is as well applicable to building panels in general. More particularly the invention relates mainly to the type of mechanically locking systems, which allow that angling of long edges and vertical movement of short edges could lock all four edges of a panel to other panels with a single action method generally referred to as vertical folding. The main principles of the invention could however also be used in other types of known mechanical locking systems as described above and below.
A floor panel of this type (FIG. 1a) is presented in WO 2006/043893 (Applicant Välinge Innovation AB), which discloses a floor panel with a locking system comprising a locking element cooperating with a locking groove, for horizontal locking, and a flexible displaceable tongue (30) cooperating with a tongue groove (20), for locking in a vertical direction. The flexible tongue as shown in FIG. 1b, bends in the horizontal plane and snaps into the tongue groove during connection of the floor panels and makes it possible to install the panels by a vertical “snap” folding or solely by a vertical movement. Similar floor panels are further described in WO 2003/016654, which discloses locking system comprising a tongue with a flexible tab. The tongue is extending and bending essentially in a vertical direction and the tip of the tab cooperates with a tongue groove for vertical locking.
Vertical locking and vertical folding of this type creates a separation pressure at the short edges when the flexible tongue or flexible parts of the tongue are displaced horizontally in a double action during the angling of the long edges. Parts of the tongue are displaced inwardly during the initial part of the locking and they are thereafter displaced towards the initial position during the final part of the locking action. The inventor has analysed several types of floor panels and discovered that there is a considerable risk that the short edges could be pushed away from each other during installation and that a gap could occur between the edge portions of the short edges. Such a gap could prevent further installation and the floor panels will not be possible to connect. It could also cause serious damage to the locking system at the short edges. Pushing the floorboards sideways towards the short edges during installation could prevent the gap. Such an installation method is however complicated and difficult to use since three actions have to be combined and used simultaneously in connection with angling down of the long edges.
It is also known, as shown in FIG. 1c that two adjacent short edges in a first row could be locked with a displaceable tongue (30) which is displaced and for example bended, as shown in FIG. 1d, by a side push at one edge section (32) when the adjacent short edges have been folded down and positioned in the same plane. Such an installation is described in DE 1020060376114B3 and a pre-published PCT application made by Välinge innovation AB. This vertical “ (side) push” folding, which generally is activated by a pressure from a long side of a third panel in a second row, displaces the separate tongue along the short edge joint but also perpendicular to the joint direction such that a part of the tongue is displaced into a groove of the adjacent short edge. This displacement perpendicular to the joint direction avoids the separation forces during the vertical folding but creates a separation force when the panels are laying flat on the sub floor and when the tongue is pressed into the tongue groove of the adjacent panel. Most vertical push folding systems, especially such systems that comprise a flexible tongue that bends in the length direction of the joint, are difficult to lock when the first and the last rows are installed.
FIGS. 2a, 2b, 2c, 3a and 3b shows examples of cross sections of known flexible tongues 30, which could be used to lock short edges according to known vertical snap folding technology. FIG. 2a shows a separate tongue 30 with a flexible snap tab extending downwards. FIG. 2b shows a separate tongue with a flexible snap tab inside a displacement groove. FIG. 2c shows a flexible tongue 30 that bends horizontally during locking according to FIGS. 1a and 1b. FIG. 3a show an embodiment of the flexible tongue, which locks with a combined turning and snapping action. Such a locking system could be locked without any separation forces. It is however difficult to produce and creates considerable resistance during locking. FIG. 3b shows a flexible tongue that is connected with pre tension into a groove and that snaps out into a tongue groove when the pre tension is released. FIG. 3c shows a flexible tongue according to FIGS. 1c and 1d that is displaced with a side pressure from one groove into an adjacent tongue groove.
Vertical folding according to known technology requires, as shown above, that some parts of the locking system, generally some parts of a separate tongue, are bended or compressed when the edges are locked. This could be avoided with wedge shaped separate tongues using the side push technology. Such wedge shape tongues consist generally of two parts or they are connected to grooves, which are not parallel with the edge. This leads to the fact that expensive materials or complicated production methods must be used.
All these known embodiments will create a separation pressure or locking resistance during installation with vertical folding. This could cause the short edges to separate such that the locking system will be damaged or such that the panels will be difficult to install. Locking strength, locking quality and production costs are in some of the known vertical locking systems not competitive with traditional mechanical locking systems installed with combinations of angling and horizontal snapping
Locking systems using the vertical folding installation method could capture a considerable larger market share if separation and resistance problems could be eliminated and if production costs and locking quality could be improved.
A major objective of the invention is to provide solutions that avoid such separation and resistance problems during locking as much as possible and where preferably non-flexible materials or tongues consisting of one separate part only could be used.
Several of the above described known locking principles and installation methods could be used in the described embodiments of the invention and the basic principles of the invention related to specific parts of the locking systems, installation and production methods are also possible to use in the known prior art locking systems.